The control of noise in the home, office, factory, automobile, train, bus, airplane, etcetera involves reducing the travel or transmission of both airborne noise and structure borne noise, whether generated by sources within or outside your environment.
Airborne noise is produced initially by a source which radiates directly into the air. Many of the noises we encounter daily are of airborne origin; for example, the roar of an overhead jet plane, the blare of an auto horn, voices of children, or music from stereo sets. Airborne sound waves are transmitted simply as pressure fluctuations in the open air, or in buildings along continuous air passages such as corridors, doorways, staircases and duct systems. The disturbing influences of airborne noise generated within a building generally are limited to areas near the noise source. This is due to the fact that airborne noises are less intense and are easier to dissipate than structure borne noise.
Structure borne noise occurs when floor or other building elements are set into vibratory motion by direct contact with vibrating sources such as mechanical equipment or domestic appliances, footsteps, falling of hard objects, objects being moved, bounced or rolled across the floor, to name a few examples. In a building for example, the vibrational or mechanical energy from one floor or wall assembly is transmitted throughout the structure to other wall and floor assemblies with large surface areas, which in turn are forced into vibration. These vibrating surfaces, which behave somewhat like the sounding board of a piano, amplify and transmit the vibrational energy to the surrounding air, causing pressure fluctuations resulting in airborne noise to adjacent areas. The intensity of structure borne noise produced by a wall or floor structure when it has been forced into vibration is generally more intense and harder to dissipate than an airborne sound wave. Unlike sound propagated in air, the vibrations of structure born noise are transmitted rapidly with very little attenuation through the skeletal frame or other structural paths of the building and radiate the noise at high levels.
Since there are so many environments such as roofing, siding, appliances, automobiles, and airplanes to name a few, where this invention can be used, we will concentrate on flooring for the remainder of this patent since there are established standards, test methods and independent testing laboratories that can test and validate floor systems for the reduction of airborne and structure borne noise. Also floors constitute an important focus for sound insulation between living areas in multi-family or single-family dwellings. Floors allow the transmission of airborne and especially structural borne noise to adjoining rooms and building structure.
In North America, acoustical consultants, architects, builders, contractors and homeowners rely on sound testing to help gauge the performance of a floor and ceiling assembly for evaluation and comparison to determine how well the floor and ceiling assembly insulates against impact and airborne noises. The International Building Code (IBC) requires minimum ratings of 50 or above for both the Impact Insulation Class (IIC) and Sound Transmission Class (STC) sound tests performed in a controlled environment to measure the amount and extent of sound vibration or noise that travels from one living area to another.
The Impact Insulation Class utilizes American Society for Testing and Measurement (ASTM) standards ASTM E 492 and ASTM E 989 for testing the ability to block impact sound by measuring the resistance to transmission of impact noise or structure borne noise by simulating footfalls, objects dropped, rolled or bounced on the floor, to name a few. The Sound Transmission Class comprises ASTM E 90 and ASTM E 413 and evaluates the ability of a specific construction assembly to reduce airborne sounds, such as voices, stereo systems, and televisions to name a few. Both tests involve a standardized noise making apparatus in an upper chamber and a sound measuring system in a lower chamber. Decibel measurements are taken at various specified frequencies in the lower chamber. Those readings are then combined using a mathematical formula to create a whole number representation of the test, the higher the number, the higher the resistance to noise.
Many condominium associations have adopted the International Building Code minimum ratings of 50 for both the Impact Insulation Class and Sound Transmission Class sound tests for floor and ceiling assemblies. It should be noted that non-laboratory, “Field” tests for Impact Insulation Class (FIIC) and for Sound Transmission Class (FSTC) are also recognized by the International Building Code. These sound tests utilize the same testing methods which are used for Impact Insulation Class and Sound Transmission Class tests but are conducted in situ in an actual building after the floor installation is completed. The International Building Code suggests ratings of 45 or higher for Field Impact Insulation Class and Field Sound Transmission Class testing.
Another test that more directly evaluates impact sound of underlayment materials is ASTM E-2179, also known as the “Delta” test. This test basically consists of two Impact Insulation Class tests conducted over the same concrete sub-floor. One test is over the bare concrete subfloor (no flooring materials) and the other is over the concrete sub-floor with floor covering material and underlayment included. The measured Impact Insulation Class values are compared to the reference floor levels defined in the standard and adjusted to provide the Impact Insulation Class the covering would produce on the reference concrete floor. The Delta Impact Insulation Class or Improvement of Impact Sound Insulation is obtained by subtracting 28 (the value for the reference bare floor from the standard) from the adjusted Impact Insulation Class of the whole assembly. As long as the same floor covering material is used, one can conduct a series of Delta tests to evaluate various underlayment materials.
It is important to note that Impact Insulation Class and Sound Transmission Class tests are not single component tests, but an evaluation of the whole floor/ceiling assembly, from the surface of the floor covering material in the upper unit, to the ceiling in the lower unit. An integral part of a report for any of these sound tests is a detailed description of the floor/ceiling assembly used in the test. The Impact Insulation Class rating of a floor should be equal to or better than its Sound Transmission Class rating to achieve equal performance in controlling both airborne and structure bore sound.
Concrete slab flooring is used extensively throughout the world in buildings and homes. A concrete slab finished with a hard surface such as ceramic tiles is the prevalent floor structure for many commercial and institutional buildings. The ceramic tiles over a concrete slab provide an aesthetically pleasing, durable and smooth surface. Because of their easy maintenance and very long durability, ceramic tiles over a concrete slab, have the lowest lifetime cost of any flooring.
On average, the concrete slab by itself has a Sound Transmission Class value around 50 and meets the International Building Code requirements. However, the Impact Insulation Class rating for typical concrete slabs is relatively low, 25 to 28 on average depending on the thickness of the concrete slab and is well below the International Building Code requirement of 50 minimum. The reason for the low Impact Insulation Class rating numbers is due to the transmission of high frequency sounds through the slab and into the room below. Hard-finish flooring materials (e.g., ceramic tiles) adhered directly to concrete slabs does not improve the Impact Insulation Class rating achieved by the concrete itself. Thus, concrete slabs finished with ceramic tiles or similar materials provide low Impact Insulation rating values and the addition of a noise reduction layer is essential to reduce impact noise for this type of extensively used floor structure.
The addition of an acoustic ceiling, if included as part of the floor and ceiling assembly, will cause an increase in both the Impact Insulation and Sound Transmission rating numbers, so the test becomes less critical when acoustic ceilings are part of the floor and ceiling assembly. Adding an acoustical ceiling to the home or office can be very expensive and adds additional labor and material costs. It would be desirable to have a floor system by itself, as defined in this patent, meet the International Building Code requirements without the added costs and labor associated with installing an acoustical ceiling.
Several methods have been used in the past to try to meet the International Building Code requirement for the Impact Insulation Class rating of a 50 minimum for the concrete slab with a hard-finish tile surface as mentioned above. One method used primarily in new construction or during renovating a structure consists of using a “floating” floor option. This method isolates the concrete slab floor from the substructure using various isolation techniques in an effort to reduce the impact noise through the floor structure as seen in FIG. 1 below.
This option is very expensive and requires extra space in renovating a building or in new construction and is not practical in many existing buildings today.
A second option used in industry today is to use a resilient layer or underlayment between the concrete slab and the hard ceramic tile finish surface in new construction or when renovating a floor in an existing building. This option is more advantageous because it is less expensive, easier to install and can be used in an existing building without reducing the overall living space of a room needed to isolate a floor structure.
There are several types of underlayments in the market used to reduce sound between a concrete slab and a hard tile surface that appears to meet the Impact Insulation Class rating of 50 minimum but each of these materials has a disadvantage. These materials are shredded or foamed rubber, natural and synthetic cork mats, natural fiber mats and modified and non-modified bituminous membranes. Shredded or foamed rubber can be very expensive, hard to install, is very heavy 1.0 to 1.4 lbs/square foot at a 6 mm thickness and it requires 6 mm of thickness to meet the Impact Insulation Class 50 minimum rating required by the International Building Codes. Cork (both natural and synthetic) and natural fiber mats can reduce the noise and approach the International Building Code requirements of 50 minimum Impact Insulation Class rating if thick enough, but these materials are not recommended for wet or humid areas since mold and mildew can develop over time and can cause health problems. Modified and non-modified bituminous membranes appear to be a good choice for use as a sound proof underlayment since they can act as a vapor barrier and are chemical resistant, easy to install, durables and are not prone to mold growth. Unfortunately, current bitumen and modified bitumen membranes in the market for floor underlayments have failed to reach the Impact Insulation Class rating of 50 minimum required by the International Building Code.
There appears to be a genuine need for a membrane that meets the International Building Code requirements for Impact Insulation Class and Sound Transmission Class ratings of 50 minimum that is easy to install that is light weight that is lower in thickness that can be used in wet or humid environments to reduce potential mold growth at a reasonable installed cost.